Extra BTU's for a Hot Water Cylinder.

[stulew]

I am going to install a new open vented conventional system with a 150 litre cylinder. My needs are as follows...
To run 13 Rads and 2 towel warmers....... Totals 20.185 Kw (68784 BTU).
I will add 10% for expansion (Not that this is really necessary because the house is at it's full potential).
How much do I have to add on to allow for the Hot water cylinder? I seem to remember a figure of 21,000BTU's. Is this correct ?. I would rather slightly over spec the boiler for this job.
Thanks For your help.

 

[Nige F]

I am going to install a new open vented conventional system with a 150 litre cylinder. My needs are as follows...
To run 13 Rads and 2 towel warmers....... Totals 20.185 Kw (68784 BTU).
I will add 10% for expansion (Not that this is really necessary because the house is at it's full potential).
How much do I have to add on to allow for the Hot water cylinder? I seem to remember a figure of 21,000BTU's. Is this correct ?. I would rather slightly over spec the boiler for this job.
Thanks For your help.

..................seem to recall 8000btu for 30 gall cyl on the Mears.........now where did I put it

 

[ollski]

3kw as far as I have been told....let you do the maths

 

[kevplumb]

3 kw 10'000

had to look in the book

think you are under tho i always do 5 kw (personal thing )

 

[ollski]

well its just the typical size, I believe the building regs (BS5449) point to 1kw per 50 litres.

 

[chrishutt]

If you have a generously sized hot water cylinder, you could not add anything to boiler output! just think about it - most of the time the boiler is oversized anyway, so there's plenty of surplus output for DHW. On those rare occasions when it's so cold that you need all output for CH, all you need to do is time the DHW function to occur when CH is off. Hot water is less likely to run out if you give yourself an extra 50 litres of storage.

 

[ChrisR]

If you want your heating on when the family of six is having consecutive showers in the morning, each emptying the cylinder, be careful. Many are now 25 kW coils. Yes that's 80,000Btu/hr or so

 

[stulew]

Thanks for the advice... I will opt for 5kw then I know that I am covered no matter what.